Ignition system with transistor control



y 1 1952 J. v. MCNULTY ET AL 3,045,148

IGNITION SYSTEM WITH TRANSISTOR CONTROL Filed Dec. 18, 1959 2Sheets-Sheet 1 F76. HHS m 4 0 13 2 6 4% 5 we g, 8 5a T T 's llllllllllJOh/I l/Mc/Vu/fy Dav/d J Wr/ghf Afforney y 1962 J. v. MONULTY ET AL3,045,148

IGNITION SYSTEM WITH TRANSISTOR CONTROL Filed Dec. 18, 1959 2Sheets-Sheet 2 Mme/Wars John M Ma Nuly Dav/dd, l l r/ %L 0 6/ By 50 TAttorney This invention relates to ignition apparatus of the capacitordischarge type, such as commonly used on jet and rocket engines.

Ignition apparatus for jet and rocket engines and the like is requiredto produce repeatedly spark discharges characterized by equalquantitiesof energy, in order that .the conditions for proper ignition at theigniter plug may be consistent from one ignition to the next. Most suchengines are used on aircraft and are supplied with electrical energyfrom a battery or other source of limited capacity. The terminal voltageavailable from such a source varies with the age out the battery andwith the magnitude of the load represented by other electrical deviceswhich may be energized from the battery concurrently with the ignitionapparatus. Other conditions may also affect the voltage available at thesource. For example,

, in one type of installation, the ignition system is required tomaintain a substantially constant energy of the spark discharge Whilethe potential of the source varies over a range from 14 to 30 volts.

It is an object of the present invention to provide ignition apparatusproducing sparks of substantially constant energy at an igniter over aconsiderable range of variation in the potential of the source ofelectrical energy.

Another object of the invention is to provide an improved ignitionapparatus of the capacitor discharge type.

A further object of the invention is to provide an improved arrangementfor charging a capacitor to predetermined potential.

The foregoing and other objects of the invention are attained in theapparatus described herein, which includes a voltage doubler consistingof an inductance element and a capacitance element connected in seriesacross a source of electrical. energy; means for discharging thecapacitor of the voltage doubler in pulses comprising a transformerprimary winding and a thyratron semiconductor device connected inseries, and means for controlling the triggering potential of thethyratron semiconductor device in response to a controlpotential'varying concurrently with the potential across the capacitanceelement of the voltage doubler. The secondary winding of the transformeris connected in series with the main ignition capacitor and supplies apulse charge to that capacitor with each triggering of the thyratrondevice. The energy stored on the main capacitor is delivered to theigniter whenever the potential across the main capacitor exceeds apredetermined value. 7

Other objects and advantages of the invention will become apparent froma consideration of the following specification and claims, takentogether with the accompanying drawings.

In the drawings:

FIG. 1 is a wiring diagram of one form of ignition apparatus embodyingour invention;

FIG. 2 is a graphical illustration of the variation in potential acrossthe voltage doubler capacitor of FIG. 1;

FIG. 3 illustrates a modification of the wiring diagram of FIG. 1;

FIG. 4 is a graphical illustration showing the effect of themodification of FIG. 3 upon the potential variation across the voltagedoubler capacitor;

FIGS. 5 to 9 are fragmentary Wiring diagrams illustrating furthermodifications of the circuit of FIG. 1;

ice

Patented July 17, 1962 FIG. 10 is a complete wiring diagram illustratinga further embodiment of the invention; Y

FIG. 10A is a wiring diagram illustrating another embodiment of theinvention; and g FIG. 11 is a fragmentary wiring diagram illustrating amodification of the circuit of FIG. 10.

FIGURE 1 This figure illustrates an ignition system which is suppliedwith electrical energy from a battery 1. A voltage doubler comprisinganinductance element 2 and a capacitance element 3 in series is connectedacross the terminals ofthe battery 1. Across the terminals .of-thecapacitor element 3 is connected a capacitor discharging circuitincluding a transformer primary winding4 and an anode. cathode path of athyratron semiconductor device, shown as a controlled rectifier orthyratron transistor 5. The

controlled rectifier 5 has an anode 5a, a gate electrode or controlelectrode 512 and a-cathode 5c. A control potential deriving networkincluding resistors 6 and 7 inseries is connected across the terminalsof capacitance element 3. The common junction of the resistors 6 and 7is connected through a wire 8 to the control electrode 5b.

The primary winding 4 is part of a transformer 9 having asecondarywinding 10. A voltage doubler capacitor 11 is connected in series with adiode 12 across the terminals of the secondary winding 10. The diode 12has its cathode connected to a junction 13, which is common OPERATION OFFIG. 1

Considering the condition in the circuit beginning at an instant whenthe capacitor 3 is completely discharged, current flowing throughinductance 2 and capacitor 3 Will cause a potential to build up on thecapacitor 3 to substantially twice the potential of the source 1. Thisphenomenon is well known and is commonly described as a voltage doubleraction. The potential across capacitor 3 is applied across the terminalsof the primary winding 4 and the anode-cathode path of the thyratrondevice 5 in series.

The thyratron device 5 is shown herein as a semi-conductor device of thetype commonly referred to as a controlled rectifier or as a thyratrontransistor. Such a device has a characteristic that its forwardimpedance, i.e., the impedance to. current flowing from.anode-to-cathode, is very high until one of two conditions occur. 'Oneof the two conditions is the occurrence of an anode-to-cathode currentgreater than a predetermined breakdown value. The other condition is theoccurrence of a current greater than breakdown value between the controlelectrode and the cathode. Upon the occurrence of either of these twobreakdown conditions, the forward impedance of the thyratron device 5drops to a very'low value and stays at that low value until theanode-to-cathode current falls to a second value substantially lowerthan the sustaining value. In the'circuit of 'FIG. 1, device 5 istripped fromits high impedance condition to its low impedance conditionwhen the current between control electrode forward impedance'ofthedevice 5 remains 'at its low value until the anode-to-cathode currentis reduced to zero.

:Resistors 6 and 7 form a voltage divider to derive from the potentialacross the capacitor 3 a proportion of that potential which is appliedthrough wire 8 to control electrode 5b as the control potential. Theresistors 6 and 7 are chosen so that the thyratron device is triggeredto its low impedance value when the potential across capacitance 3approaches a value 2E, as shown in FIG. 2, B being the potential of thebattery 1.

When the thyratron devie -5 is triggered, a pulse of current flows fromcapacitance 3 through the primary winding 4, a corresponding pulse beingthereby induced in secondary winding 10. The latter pulse charges thecapacitor 1 1. The polarity of the windings 4 and is indicated by thedots in the drawing. The pulse produced in the winding 10 has itspositive polarity at the upper terminal of that winding. This pulseflows through capacitor 11, diode \14 and capacitor and tends to chargethe capacitors 11 and 15. The pulse does not flow through diode '12,since diode 12 has its high impedance opposed to the pulse.

On the half-waves when the upper terminal of the secondary winding 10 isnegative, current flows from that winding through the diode 12 andcharges the capacitor 11 with its right-hand terminal positive. Thewinding 10 and capacitor 11 together act as a voltage doubler, todevelop across the capacitor 11 a transient inverse potential equal totwice the applied potential. On the opposite half-waves, current fiowthrough the diode 12 is blocked but current can flow from winding 10 andcapacitor 11, which now act as potential sources in series aiding,through diode 14 and capacitor 15, thereby charging capaciotr 15. Whenthe charge on capacitor 15 exceeds a value determined by the breakdownpotential of gap 16, that gap breaks down. Thereupon, substantially thefull potential of capacitor 15 appears across the resistor 17 and gap 18in parallel. The gap 18 in turn breaks down, whereupon the capacitor 15discharges through it.

The discharging of the capacitor 5 is repeated each time that the chargeon it builds up sufficiently to break down the gap '16.

The circuit goes through a series of pulse producing cycles as describedabove. Fig. 2 shows at the variation of potential across capacitor 3during such cycles. During the capacitor discharging phase of eachcycle, theinductance in the circuit tends to maintain the flow ofcurrent even after the capacitor is discharged, with the result that thecapacitor begins to charge in the reverse direction, resulting in thenegative excursion of potential appearing at 20b in FIG. 2. Eventuallythis reverse potential blocks the current flow through the thyratrondevice 5, which thereupon returns to its high impedance condition andthe cycle begins again. During each of these cycles, a pulse of currentcharges the capacitors 11 and 15. Capacitor 11 cooperates with winding10 to form a voltage doubler, so that capacitor 15 is charged at ahigher potential. As the series of pulse cycles continues, the potentialacross the capacitor 15builds up in a seires of steps. The potentialacross storage capacitor 15 is applied across the sealed gap 16. Therebeing then no current flow through resistor '17, susbtantially the fullpotential across capacitor 15 is applied across the sealed gap 16. Thebreakdown potential of the gap 16 is made somewhat higher than thebreakdown potential of the igniter gap 18. When the potential of thecharge on capacitor 15 exceeds the breakdown potential of the gap 16,the charge on capacitor 15 is discharged through the trigger gap 16 andthe igniter gap 18. The gap 18 has a substantially lower impedance thanthe resistor 17 and takes substantially all the current flowing from thecapacitor 15. The breaking down of the gaps 16 and 18 produces a lowimpedance path to the charge stored on the capacitor 11, and that chargenow also flows through the gaps 16 and 18.

It may be seen that the circuit of FIG. 1 provides a series of sparkdischarges at the igniter 18. Each of those spark discharges is built upby a series of pulses of substantially equal energy applied to thecapacitors 11 and 15, so that each spark discharge at the igniter gap 18has substantially the same energy. Although the potential of the source1 may vary, the characteristics of the thyratron device 5 do not vary.The breakdown control potential on electrode 5b, at which the thyratrondevice 5 shifts from its high impedance to its low impedance condition,is always the same, being determined by the characteristics of thedevice 5 and not by the charge stored on capacitor 3. The magnitude ofthe current pulses which charge the capacitors 11 and :15 is therebymade independent of the potential of the source. The trigger gap 16consequently always breaks down after the same number of charging pulsesand the charge built up on the capacitors 11 and 15 and dischargedthrough the igniter gap 18 alawys has susbtantially the same energy.

FIGURES 3 AND 4 FIG. 3 illustrates a modification of the circuit ofFIG. 1. In accordance with this modification a diode 19 has its anodeconnected to the cathode of the thyratron device 5, while its cathode isconnected to the anode of the thyratron device 5. The presence of thediode 19 limits the reverse polarity potential across the controlledrectifier 5 to the forward impedance drop across diode 19. The operationas modified by diode 19 is illustrated by the curve 20A in FIG. 4. Thediode 19 makes the potential from which the capacitor 3 starts to chargemore positive. The current for recharging the capacitor 3 from thereverse potential value shown at 20b to a positive value must besupplied by battery 1. When the diode 19 is added as in FIG. 3, thisreverse potential is smaller, so that the recharging current is smaller,and hence the circuit losses are lower. The etficiency of the circuit isthereby improved.

The presence of diode 19 also prevents any tendency to build up apotential on the capacitor 3 gradually over several cycles, because ofincomplete discharge of the capacitor on each cycle.

FIGURE 5 This circuit is modified from that of FIG. 1 by thesubstitution of a saturable core transformer 21 in the control potentialderiving network, in place of the resistors 6 and 7 of FIG. 1.Transformer 21 has a primary winding 22 and a secondary winding 23.Primary winding 22 is connected between the ungrounded terminal 24 ofcapacitor 3 and the control electrode 5b. Secondary winding 23 isconnected between the anode ofthe diode 19 and ground.

OPERATION OF FIG. 5

During charging of thecapacitor 3 the secondary winding 23 issubstantially open circuited, due to the diode 19, which has its highimpedance in series with Winding 23. The current flowing through winding22 and control electrode 5b increases as the charge on capacitor 3increases, finally saturating the core of transformer 21, whereupon apulse of current flows through control electrode 5b, setting off adischarge of capacitor 3 through the thyratron device 5. When thethyratron device 5 breaks down to its low impedance value, the capacitor3 is discharged and the potential across it reverses as the magneticfield of the inductance 2 collapses. This reverse potential sends a highcurrent through the secondary winding 23 and diode 19, resetting thecore of transformer 21 by saturating it in the opposite sense, therebyrestoring primary winding 22 to its high impedance condition.

FIGURE 6 a3 network including a resistor 26 and a capacitor 27. A switch28 connects the time constant network in series between the junction 24and'ground. The switch 28 is movable from the position shown to a secondposition in which the time constant network is connected across abattery29.

OPERATION OF FIG. 6

The timing between the start of a cycle atzero potential across.capacitor 3 and the breaking down of the thyratron device 5 iscontrolled in FIG. 6 by the time characteristics of the network 26, 27rather than by the time characteristics of the capacitor 3 itself. Whenthe switch 28 is in its right hand position, as shown, the timecharacteristics of the network 26, 27 are superimposed on the timecharacteristics of the voltage doubler, i.e., the potential applied tothe network 26, 27 is supplied from the capacitor 3. When the switch28is thrown to its left-hand position, the triggering time of thethyratron device 5 is determined only by the time characteristics of thenetwork 26, 27 and the potential ofthe battery 29. If this battery isprovided to supply this network only, then its characteristics may bemuch more closely controlled and remain much more stable than thecharacteristics of the main battery 1 which supplies energy for thetrigger gap and perhaps for other load devices.

The characteristics of the double base diode 25 are such that itsimpedance is high until such time as a predetermined potential isapplied to control electrode 25c, at which time the impedance betweenthe control electrode 250 and base 25b drops to a very low value.Capacitor 27 then discharges through this low impedance, producing anoutput pulse.

FIGURE 7 This figure illustrates a modification of the circuit of FIG.6- and shows a different arrangement for supplying potential to theterminals of the time constant network 26, 27. In FIG. 7, the battery 1is used tosupply current through a resistor 31 and a reverse biaseddiode 32. The diode'32 is of the Zener voltage type and has aces, 14s

the increased energy per pulse due to the increased battery potential.

FIGURE 8 This figure shows a modification of the circuit of FIG. 7, inwhich a resistor 33 is added between the Zener diode 32 and theterminfls of the time constant network. This circuit, by virtue of thepotential drop due to current flowing in resistor 33, varies thepotential applied to the time constant network as a function of thebattery potential. In other words, an increase in the battery potentialincreases the potential applied to the time constant network andconsequently makes the capacitor 27 charge toits tripping value in ashorter time.

It has been found that the circuit of FIG. 7 tends to overcompensate foran increase in battery potential. In other words, as the batterypotential increases, it slows down the pulse rate so much that the poweroutput is actually decreased. In order to correct that unbalance, theresistor 33 has been added in the circuit of FIG. 8. Be-

1 cause of the resistor 33, the potential across the time con stantnetwork 26, 27 is not fixed, but increases with an increase in thepotential of battery 1, due to the potential drop across resistor 33. Byproperly balancing the potential drop across resistor 33 with respect tothe potential across battery I, the circuit of FIG. 8 may be made tocompensate for the changes in the battery potential,

, soias to maintain a close control of the power output,

a high impedance in its reverse direction until a predeter-v minedpotential is exceeded. The impedance then becomes very low andefiectively fixes the potential at that predetermined value. Thepotential across the diode 32 and hence across the time constant networkis thereby fiXed at a ,very definite value.- v i i The ideal operationin circuits of the type disclosed herein is to maintain'the powerdelivered to capacitor 15 substantially constant, regardless of changesin the potential of the battery 1. An increase in the potential ofbattery 1 tends to increase the energy output per pulse of the capacitor3. A compensating elitect'may be provided by arranging the triggeringsystem which times the pulses from the capacitor 3 so that an increasein the battery potential tends to decrease the pulse rate. If thedecrease in the pulse rate exactly balances the increase in the energyper pulse, then a substantially constant power output may be produced,even though the battery potential changes. u

In the circuit of FIG. 7, the battery potential is applied across thebase electrodes 25a and 25b of the double base diode 25. An increase inthis potential requires a higher potential on the control electrode 250to trip the double base diode to its low impedance value. The potentialof control electrode 250 is determined by the time constant network 26,27, which is now supplied by the constant potential across diode 32.Capacitor 27 therefore charges at the same rate, regardless of changesin the potential of battery 1. However, since an increase in the batterypotential requires a higher potential at electrode 250 to trip thedouble base diode, a longer charging time for capacitor 27 is required.before the diode 25 trips.

The pulse rate is thereby reduced to compensate for at least overlimited ranges of variation in the potential of battery 1.

As a further alternative, the voltage dividers of FIGS. 7 and 8 may beconnected across capacitor 3 instead of across battery 1.

FIGURE 9 is determined by the characteristics of the Zener diode 34.

FIGURE 10 This circuit is considerably modified from the previouscircuits, particularly in the potential supply for the time constantnetwork which controls the discharge times, the connections of the diode19, and in the circuitry connected to the secondary winding 10.

The potential supply for the time constant network '26, 27 is obtainedthrough a filter including an inductance element 35 and a capacitanceelement 36 connected in parallel with the voltage doubler 2, 3 butotherwise independent of it. The potential appearing across capacitor 36is applied to a voltage divider network including resistor 37 andresistor 38 and a Zener voltage diode 39 similar to the network shown inFIG. 8 above. Thevoltage divider network 37, 38, 39 is utilized tocontrol the variation of outputpower with changes in the batteryvoltage.The variation may be controlled over a wide range, using the principlesdiscussed above in connection with FIG. 8. The potential across theresistor 38 and diode 39 in series is appliedacross the time constantnetwork 26, 27. The junction between inductance 35 and capacitor 36 isalso connected through a'resistor 40 to the base 25a of the double basediode 25. By virtue of these arrangements, the time intervals at whichthe thyratron device 5 is triggered are determined by the time constantnetwork and are not aifeoted by transient conditions existing in themain spark energy supply circuit. The elements used in the controlvolt-age deriving network, may, therefore, be more precisely selectedand controlled as to their impedance values, since they do not have tocarry the heavier potential on capacitor 3, so that the losses in thecircuit are decreased. The utilization of the energy from the capacitor3 is thereby made considerably more efiicient. The circuit through thesecondary winding 10 includes a diode 42, a capacitor 43' and a resistor44 in series. Diode 42 acts as a half-wave rectifier, to determine thepolarity of the charge on capacitor 43. An igniter gap 45 of thesemiconductor type is connected across the resistor 44. A trigger gap 46is connected between ground and the common junction of diode 42 andcapacitor 43.

The energy to be discharged at the gap 45 is stored on the capacitor 43.When the potential on capacitor 43 exceeds the breakdown potential ofthe sealed gap 46, the energy on the capacitor 43 is discharged througha circuit consisting only of that capacitor and the gaps 45 and 46.

FIGURE 10A The circuit shown in this figure is based on that in FIG. 10,but has been improved by the addition of several elements. This is thepresently preferred embodiment of the'invention.

The elements added in this figure include a diode 70, a transformer 71having a primary winding 72 and a secondary winding 73, a diode 74, acapacitor 75', a capacitor 76, a diode 77, and a resistor 78.

Diode 70 is eifective to hold the charge on capacitor 3 if it reachesfull charge before the triggering pulse is applied to the thyratrondevice 5.

Transformer 71 is a step-up transformer, and is effectiveatlowervoltages to improve the tripping or starting characteristics. That is tosay, it permits the circuit to trigger the transistor at a lower voltageof battery 1.

Diode 74 prevents reverse potential due to overshoot in transformer 71from reaching the control electrode 5b of thyratron device 5.

Capacitor 75 provides a minimum capacitive load for thyratron device 5,and thereby prevents certain undesirable conditions which mightotherwise occur in the case of an open circuit or high resistance loadon the secondary winding 10. Such an open circuit condition wouldincrease the impedance of primary winding 4 to the capacitor dischargecurrent to a very high value, which would tend to delay thecapacitordischarge and spread out the charging pulse. The capacitor 65establishes a maximum impedance limit on the primary winding 4, andensures that capacitor 3 will discharge on each pulse.

Capacitor 76 and diode 77 cooperate with secondary winding to form avoltage doubler, functioning in a manner generally similar to thecapacitor 11 and diode 12 of FIG. 1.

Resistor 78 is provided to protect diodes 77 and 42 from overcurrents inthe forward direction which might occur during oscillatory dischargesthrough the gap 45.

FIGURE 11 The circuit illustrated in FIG. 11 shows a different form ofmechanism for controlling the potential supplied to the controlelectrode 5b of the controlled rectifier 5. This circuit is in otherrespects similar to that shown and described in FIG. 10. Those elementswhich correspond, both as to structure and function, to theircounterparts in FIG. 10, have been given the same reference numerals.

The circuitry for supplying a potential to control electrode 5b includesa first voltage divider connected across the terminals of the battery 1and traceable through a resistor 46a, a resistor- 47, a capacitor48,'and a transformer winding 49 to ground at 50. A capacitor 51 isconnected in'parallel with resistor 46a. A second voltage divider isalso connected across the battery l-and includes resistors 52 and 53 inseries. A capacitor 54 is connected across the resistor 53.

A transistor 55 has an emitter electrode 55a, a base electrode 55b, anda collector electrode 55c. In the preseut circuit, the base serves asthe input electrode, the emitter as the output electrode, and thecollector as the common electrode. Collector 55c is connected to thejunction 56 between resistors 46 and 47. Base electrode 55b is connectedto the opposite terminal of resistor 47. Emitter electrode 55a isconnected through a secondary winding 57 of a transformer 58 to thecommon junction 59 of resistors 52 and 53. Transformer 58 has an outputwinding 60 having one terminal connected to ground and the otherconnected through a wire 61 to the control electrode 5b. A Zeuer diode62 is connected between junction 56 and ground.

FIGURE 11-OPERAT'ION to the igniter 45 substantially constant, thetriggering sys- V tern which times the pulses from the capacitor 3 ismade to respond to an increase in the battery potential in such a manneras to decrease the pulse rate. The increase in energy per pulse iscompensated by the decrease in pulse rate, resulting in a substantiallyconstant power output.

The circuit, including transistor 55, transformer 58, and relatedelements may be described as a blocking oscillator. It operates to applyperiodically to the control electrode 5b potentials which are effectiveto trigger the controlled rectifier 5 to its low impedance value,thereby producing an output pulse through the transformer 9.

The transistor 55 is shown as an NPN type, so that it is held off by anemitter potential more positive than the base potential, and is turnedon by an emitter potential more negative than the base potential.

The Zener diode 62 fixes the potential at junction 56 and collector 55cwith respect to ground. The impedances of resistors 52 and 53 areselected so that when the transistor is not conducting the junction 59is negative with respect to junction 56.

When power is first applied to the circuit, emitter 55e is substantiallyat the potential of junction 59, since there is then no current flowthrough or potential induced in the winding 57. Base 55b is connectedthrough the uncharged capacitor 48 to ground, there being substantiallyno potential across winding 49. Base 55b is therefore more negative thanemitter 55a, and the transistor is off. The capacitor 48 immediatelystarts to charge through resistors 46 and 47, and its terminal nearestthe resistor 47 swings in a positive sense, eventually becoming morepositive than the potential of emitter 552, whereupon the transistorstarts to conduct. I

As the current flow through emitter 552 increases, it passes throughprimary winding 57, inducing a potential in secondary winding 49 of apolarity tending to charge capacitor 48 reversely, i.e., with its lowerterminal positive. This charging current flows through base 55b andtends to drive the transistor to conduct more strongly. Finally, thecharge on capacitor 48 reaches a condition of balance with the potentialacross secondary winding 49, and the charging current stops. Thepotential stored on capacitor 48 is then etfective to swing base 55b ina negativesense, thereby cutting off the transistor 55. Current thenstops flowing through winding 57. The charge on capacitor 48 then holdsthe transistor off until that charge is dissipated by current suppliedthrough resistors 46 and 47. The cycle then repeats. The pulse ofcurrent in winding 57 induces a potential in winding 60, where it iseliective to control the thyratron device 5.

If the potential of battery 1 increases, the potential of 9 v a junction59 swings more positive, while the potential of junction 56 remainsfixed at a value morepositive than junction 59. The emitter potential,when the transistor is ofif, is substantially the same as that ofjunction 56. Hence, in order to turn the transistor on, the capcitor 48must charge to a more positive potential to make the base 55b morepositive than emitter 55a This charging of capacitor 48 to a higherpotential takes a longer time, with a consequent decrease in the rate ofsupply of tripping pulses to the thyratron device 5. The increase inpulse energy is compensated by the decrease in the pulse rate, so thatthe power output remains substantially constant.

While I have described the operation of the invention, with respect toits constant power output characteristics, in terms of an increase inbattery potential, it should be apparent that a decrease in batterypotential produces an analogous but reverse operation, with acompensating increase in the pulse frequency, and a similar ultimateresult, i.e., constant power output spark energy at the igniter.

Resistor 46a is provided to limit the current flow 7 through the diode62.

Capacitor 51 provides a low impedance path to alternating cur-rent, sothat resistor 46a does not limit the operation of the blockingoscillator. Capacitor 54 provides a similar alternating current by-passaround resistor 53, so that during pulsing of the blocking oscillator,resistors 46 and 53 are by-passed, and the full battery potential iseffective between the emitter and collector of the transistor. 1

The following table shows a suggested set of values which will work inthe circuit of FIG. 11. Obviously, the invention is not limited to anyof these values.

Table Resistor 46a ohms 500 Resistor 47 do 4000 Capacitor 48 mfd 0.1Resistor 52. ..ohms 10,000 Resistor 53 .do 1,000

It should be understood that the. circuits shown and described maintainthe power output to capacitor 15 substantially constant only over alimited range of variation of the potential of battery 1. Given aparticular range of source potential, however, it is easy to design acircuit following the invention which will hold the power outputconstant.

While we have shown and described certain preferred embodiments of ourinvention, other modifications thereof will readily occur to thoseskilled in the art, and we therefore intend our invention to be limitedonly by the appended claims.

We claim: v

1. Capacitor charging apparatus COIIlPl'lSlllg a source ofunidirectional electrical energy, an inductance element and acapacitance element connected in series across the source, a transformerhaving a primary winding and a secondary winding, a thyratronsemiconductor device having an anode, a cathode, and a gate electrode,means connecting the primary Winding and the anode-cathode path of thethyratron semiconductor device in series across the capacitance element,a capacitor to be charged, an asymmetrically conductive device, meansconnecting the capacitor and the asymmetrically condutcive device inseries across the secondary winding, means for deriving a controlpotential varying concurrently with the potential across the capacitanceelement, and means connecting the control potential deriving means tothe'gate electrode to trigger a pulse discharge through the thyratronsemiconductor device whenever the capacitance element is charged to apredetermined potential, whereby thecapacitor is charged by repeatedpulses of substantially equal energy; an electric'circuit branchconnected in parallel with the electric path through the anode andcathode of the thyratron semiconductor device, and a diode connected insaid branch and having its anode and cathode respectively connected tothe cathode and anode of the thyratron semiconductor device, saidcircuit branch being effective after each discharge of the capacitanceelement through the thyratron semiconductor device to pass anoscillatory current of the opposite polarity.

2. Capacitor charging apparatus as defined in claim 1, including meansdirectly and conductively connecting the anode and cathode of the dioderespectively to the cathode and anode of the thyratron semiconductordevice.

3. Capacitor charging apparatus as defined in claim 1, in which saidcircuit branch includes an inductor in series with the diode, and meansconnecting the terminals of the branch to the respective terminals ofthe capacitance element.

4. Capacitor charging apparatus as defined in claim 1, in which saidcontrol potential deriving means comprises a saturable core transformerhaving a primary winding and a secondary winding; said means connectingthe control potential to the gate electrode connects the primary Windingof the saturable core transformer between the gate electrode and theterminal of the first-mentioned transformer primary winding farthestfrom the thyratron semiconductor device, and said branch circuitincludes the secondary winding of the saturable core transformer inseries with the diode.

5. Capacitor charging apparatus comprising a source of unidirectionalelectrical energy, an inductance element and a capacitance elementconnected in series across the source, a transformer having a primarywinding and a secondary Winding, a thyratron semiconductor device havingan anode, a cathode, and a gate electrode, means connecting the primarywinding and the anode-cathode path of the thyratron semiconductor devicein series across the capacitance element, a capacitor to be charged, anasymmetrically conductive device, means connecting the capacitor and theasymmetrically conductive device in series across the secondary winding,means for deriving a control potential varying concurrently with thepotential across the capacitance element, and means connecting thecontrol potential deriving means to the gate electrode to trigger apulse discharge through the thyratron semiconductor device whenever thecapacitance element is charged to a predetermined potential, whereby thecapacitor is charged by repeated pulses of substantially equal energy;said control potential deriving means comprises a double base diodehaving two base electrodes and a control electrode, means connecting onebase electrode to the terminal of the transformer winding farthest fromthe thyratron semiconductor device, a time constant network comprising aresistor and a capacitor in series, andmeans connecting the commonterminal of the resistor and capacitor to the control electrode; andsaid means connecting the control potential deriving means to the gateelectrode comprises a connection between the other base electrode andthe gate electrode.

6. Capacitor charging apparatus as defined in claim 5, in which saidcontrol potential deriving means includes a separate source ofelectrical energy, and means connecting said time constant networkacross the separate source.

7. Capacitor charging apparatus as defined in claim 5, in which saidcontrol potential deriving means includes means connecting the timeconstant network across the capacitance element.

8. Capacitor charging apparatus as defined in claim 5, in which saidnetwork includes a second resistor and a diode in series, and meansconnecting the first-mentioned resistor andthe capacitor in seriesacross the diode.

9. Capacitor charging apparatus as defined in claim 5, in which saidnetwork includes a second resistor, a third resistor and a 'diodeconnected in series, and means con- 1 2t necting the first-mentionedresistor and the capacitor across the third resistor and the diode.

l0. Capacitor charging apparatus as defined in claim 9, in which saidnetwork includes filter comprising a second inductance element and asecond capacitance element connected in series across the source, andthe second and third resistors and the diode are connected in seriesacross the second capacitance element.

11. Capacitor charging apparatus comprising a source of unidirectionalelectrical energy, an inductance element and a capacitance elementconnected in series with the source, a transformer having a primarywinding and a secondary winding, a thyratron semiconductor device havingan anode, a cathode, and a gate electrode, means connecting the primarywinding and the anode-cathode path of the thyratron semiconductor devicein series across the capacitance element, a capacitor to be charged, anasymmetrically conductive device, means connecting the capacitor and theasymmetrically conductive device in series across the secondary winding,means connected across the source in parallel with the series-connectedinductance and capacitance elements for deriving a control potentialvarying concurrently with the potential across the capacitance element,and means connecting the control potential deriving means to the gateelectrode to trigger a pulse discharge through the thyratronsemiconductor device whenever the capacitance element is charged to apredetermined potential.

12. Capacitor charging apparatus as defined in claim 11, wherein saidcontrol potential deriving means comprises a second inductance elementand a second capacitance element connected in series across the source,and a time constant network connected between the common terminal ofsaid second inductance and second capacitance elements and one terminalof said source.

13. Capacitor charging apparatus as defined in claim 11, in which saidcontrol potential deriving means includes a blocking oscillator.

14. Capacitor charging apparatus as defined in claim 13, in which saidcontrol potential deriving means comprises two voltage dividersconnected across said source, and said blocking oscillator comprises atransistor having input, output and common electrodes, a transformerhaving a primary winding, an output secondary winding and a feedbacksecondary winding, means including said primary winding connecting saidtransistor output electrode to a point on one of said voltage dividers,means including said feedback winding connecting the input electrode ofthe transistor to one terminal of said source, means connecting thecommon electrode of the transistor to the other voltage divider, andmeans connecting the output secondary winding to the gate electrode ofthe thyratron semiconductor device.

15. Capacitor charging apparatus comprising a source of unidirectionalelectrical energy, an inductance element and a capacitance elementconnected in series across the source, a transformer having a primaryWinding and a secondary winding, a thyratron semiconductor device havingan anode, a cathode, and a gate electrode, means connecting the primarywinding and the anode-cathode path of the thyratron semiconductor devicein series across the capacitance element, a capacitor to be charged, anasymmetrically conductive device, means connecting the capacitor and theasymmetrically conductive device in series across the secondary winding,means for deriving a control potential varying concurrently with thepotential across the capacitance element, and means connecting thecontrol potential deriving means to the gate electrode to trigger apulse discharge through the thyratron semiconductor device Whenever thecapacitance element is charged to a predetermined potential, whereby thecapacitor is charged by repeated pulses of substantially equal energy;said control potential deriving means comprising a double base diodehaving two base electrodes and a control electrode, means connecting onebase electrode to the terminal -of the transformer winding farthest fromthe thyratron semiconductor device, a time constant network comprising aresistor and a capacitor in series, and means con necting the commonterminal of the resistor and capacitor to the control electrode; andsaid means connecting the control potential deriving means to the gateelectrode comprises a step-up transformer having a primary windingconnected between the other base electrode and a common terminal and asecondary winding connected between the common terminal and the gateelectrode.

16. Capacitor charging apparatus as defined in claim 15, including adiode connected in parallel with the secondary winding and poled toblock passage of current to the gate electrode due to overshoot of thetransformer.

17. Capacitor charging apparatus comprising a source of unidirectionalelectrical energy, an inductance element and a capacitance elementconnected in series across the source, a transformer having a primarywinding and a secondary winding, a thyratron semiconductor device havingan anode, a cathode, and a gate electrode, means connecting the primarywinding and the anode-cathode path of the thyratron semiconductor devicein series across the capacitance element, a capacitor to be charged, anasymmetrically conductive device, means connecting the capacitor and theasymmetrically conductive device in series across the secondary winding,means for deriving a control potential varying concurrently with thepotential across the capacitance element, and means connecting thecontrol potential deriving means to the gate electrode to trigger apulse discharge through the thyratron semiconductor device whenever thecapacitance element is charged to a predetermined potential, whereby thecapacitor is charged by repeated pulses of substantially equal energy; asecond capacitor connected in parallel with the secondary winding andeffective to provide a substantial capacitive load on the thyratronsemiconductor device under high impedance conditions in said seriesconnecting means.

18. Capacitor charging apparatus as defined in claim 11, in which saidcontrol potential deriving means includes control pulse producing means,and means responsive to the source potential for varying the rate ofproduction of control pulses to reduce said' rate as the sourcepotential increases and increase said rate as the source potentialdecreases.

l9. Capacitor charging apparatus, comprising a source of unidirectionalelectrical energy, an inductance element and a capacitance elementconnected in series across the source, a transformer having aprimary-winding and a secondary winding, a thyratron semiconductordevice having an anode, a cathode, and a gate electrode, meansconnecting the primary winding and the anode-cathode path of thethyratron semiconductor device in series across the capacitance element,a capacitor to be charged, an asymmetrically conductive device, meansconnecting the capacitor and the asymmetrically conductive device inseries across the secondary winding, a diode connected between the gateelectrode and the terminal of the transformer primary winding farthestfrom the thyratron semiconductor device, said diode being poled topresent its high impedance to the potential across the capacitanceelement, said diode being effective when the last-mentioned potentialexceeds the breakdown potential of the diode to transmit a trigger pulseto the gate electrode and thereby to trigger a pulse discharge throughthe thyratron semiconductor device whenever the capacitance element ischarged to the diode breakdown potential, whereby the capacitor ischarged by repeated pulses of substantially equal energy.

References Cited in the file of this patent UNITED STATES PATENTS2,027,617 Randolph Jan. 14, 1936 (Gther references on following page) 142,907,929 Lawson Oct. 6, 1959 FOREIGN PATENTS 1,054,505 Germany Apr. 23,1959 OTHER REFERENCES Transistor Power Supplies, by L. H. Light,Wireless World, December 1955; pages 582 to 586.

